The classification and analysis of fogs at the Beijing Capital International Airport (BCIA) are made based on the statistical analysis of the hourtohour fog observation data and the AWOS (Automatic Weather Observation System) data from BCIA from 1999 to 2006 (including wind, temperature, pressure, relative humidity and visibility). Each type of fog is statistically studied from the aspects of the temporal and background characteristics, pressure and wind variation characteristics, etc., during the occurrence and dissipation of fogs. The results show that radiation fogs occur most frequently at BCIA, before which there appears a gradually increasing humidity with the wind direction being SE or NNE. Advection fogs form generally after the rapid increase of humidity and the rapid decrease of visibility, inducing most serious damage to flighting, of which 81.8% reached the heavy fog standards. Front fogs occur mostly before a cold front, being persistent, mostly along with an advection or radiation process, appear usually earlier than radiation fog, mostly in the later afternoon and evening with a longer duration,and disperse generally after the front.